Add error handling for missing `parser` gem in `Prism::Translation`

[koic]

Resolves #2803.

This PR adds error handling for missing parser gem in Prism::Translation.

The parser gem is a required runtime dependency when using Prism::Translation::Parser. But it is not required for other uses of Prism. To avoid unnecessary dependencies, it is not added as a runtime_dependency in the prism.gemspec. Instead, if the dependency is missing, instructions are given to add it to Gemfile.

Before

$ bundle exec ruby -e 'require "prism"; require "prism/translation/parser33"'
/Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require': cannot load such file -- parser (LoadError)
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser.rb:3:in `<top (required)>'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:6:in `<module:Translation>'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:4:in `<module:Prism>'
from /Users/koic/src/github.com/ruby/prism/lib/prism/translation/parser33.rb:3:in `<top (required)>'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `require'
from /Users/koic/.rbenv/versions/3.3.1/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
from -e:1:in `<main>'

After

$ bundle exec ruby -e 'require "prism"; require "prism/translation/parser33"'
Error: Unable to load parser. Add `gem "parser"` to your Gemfile.